\documentclass[11pt]{article}

\begin{document}

SomeIntro
\begin{theorem}
\begin{lemma}
$12345$$$54321$$
\end{lemma}
$3+4$
\end{theorem}
$x=5t$

\begin{proof}
\begin{lemma}
Lemma1
\end{lemma}
\begin{lemma}
Lemma2
$someFormula$
\end{lemma}
\end{proof}

\end{document}